The more I talk to homeopaths and other alternative medicine practitioners, the more I realise that the distinction between in vitro and in vivo testing is unclear to many.
It may be due to ignorance, or it may be in a desperate bid to pad out the lack of real-life clinical evidence, or to stun us all into silence with impressive looking sciencey stuff, but it seems that alternative medicine supporters are desperate to throw in vitro studies my way as "evidence" that their treatments work. But here's the thing: it's not evdience that it works at all. In fact, for the purposes of informing treatment decisions, any in vitro data might as well be discarded before you even bother reading it.
Why do i say this? Well, the easiest way to explain this is in picture form (drawings are courtesy of Haymond) :
As you can see from these pictures, a few cells in a petri dish actually look (and act) rather differently to a functioning, whole human body. So positive (or negative) results in an in vitro study actually bear very little resemblance to real life clinical situations. What in vitro testing is great for is as preliminary evidence- to make new discoveries and to guide further research, and to find out the all-important details of how something may work. But we can't use some cells in a petri dish to say "Yes, this will definitely work for this or that illness". The only sort of evidence that we can use to decide if a drug is effective in any particular illness is a robustly designed clinical trial, and even then we can't use that as a cast iron guarantee.
I'm hoping that you will forgive me for this horrendous oversimplification, but it is hopefully a useful point to make. So, the next time you come across some in vitro studies being used as "evidence" that homeopathy works, you know that they're actually scraping the barrel, particularly gievn the fact that homeopathis is supposed to have been around for 2000 years. I'd expect after that amount of time that they'd have more than cell culture studies to their name.